The present invention relates to a piezoelectric thin-film element and an ink-jet recording head using the same.
Conventionally, for example, in an ink-jet recording head or the like, an oscillator acting as a driving source for jetting ink is constituted by a piezoelectric thin-film element. Generally, this piezoelectric thin-film element has a structure provided with a piezoelectric thin film comprising polycrystal, and upper and lower electrodes disposed so as to hold this piezoelectric thin film therebetween.
This piezoelectric thin film is generally composed of a two-component system mainly containing lead zirconate titanate (hereinafter abbreviated to "PZT"), or a three-component system in which a third component is added to the PZT of this two-component system. The piezoelectric thin film having such a composition can be formed, for example, by a sputtering method, a sol-gel method, a laser ablation method, a CVD method or the like.
In addition, examples of conventional technique particularly relating to the present invention are disclosed in U.S. Pat. No. 5,265,315, and National Patent Publication No. Hei-5-504740.
In these conventional examples, after a silicon dioxide film is formed to be 2,500 .ANG. on a monocrystal silicon substrate by a thermal oxidation method, a lower electrode layer of aluminum, nickel, chrome, platinum or the like is laminated thereon with a thickness of about 0.2 .mu.m. Next, a PZT film as a piezoelectric element is laminated on the lower electrode layer with a thickness of 2 to 10 .mu.m by a sol-gel method. Next, after an upper electrode is laminated on this PZT film, a desired process such as etching, or the like, is effected selectively from the back surface of the monocrystal silicon substrate to thereby form an ink chamber. In such a manner, an ink-jet recording head is formed.
Such an ink-jet recording head is disposed in a printer or the like. Today, however, higher resolution is requested to be realized.
In order to improve such resolution of a printer, for example, it is considered to reduce the size of the ink chamber, or to make the thickness of the piezoelectric film thinner.
However, in the above-mentioned structure and manufacturing methods, if the thickness of the piezoelectric film is made to be 5 .mu.m or less, the boundary adhesion between the silicon dioxide film and the lower electrode film or between the lower electrode film and the PZT film is so reduced that there arises a problem that the reliability is deteriorated by the separation of the PZT film, the floating of the PZT film caused by the stress of the silicon dioxide film, and so on.
In addition, in order to obtain desired capacity of ink jetting, it is preferable to make the composition of the piezoelectric film not two-component PZT but three-component PZT.
However, when the composition of the piezoelectric film is made to be three-component PZT, it is necessary to make PZT be subjected to heat treatment at burning temperature of 800.degree. C., so that there is a problem that the adhesion between the lower electrode film and the PZT film is reduced.